Technical Field
The present invention relates to an image projection apparatus, and a method of controlling an image projection apparatus, and a storage medium of program.
Background Art
Image projection apparatuses known as projectors have been widely used with the advancement of higher resolution of liquid crystal panels, enhancement of brightness of lamps due to higher efficiency, and lower price. Further, light-weight and compact image projection apparatuses using digital micro-mirror devices (DMD) as an image generation element have been widely used in offices, schools, and homes.
The image projection apparatuses can employ various lamps as a light source. For example, an arc lamp such as high pressure mercury lamp can be used. When the high pressure mercury lamp is used as the light source, the image projection apparatus requires several minutes to set desired brightness for a projection image to be projected by the image projection apparatus. Specifically, it takes about several minutes from a time point of supplying power to the image projection apparatus to a time point of activating the light source with a given driving power level, in which brightness of projection image becomes gradually brighter until the projection image is being projected with desired brightness. Hereinafter, this time period may be referred to warming-up mode.
Further, when the image projection apparatus is set on a given place, a suitable focus position of the image projection apparatus varies depending on the distance between the image projection apparatus and a projection face (e.g., screen). Therefore, the focus position is required to be adjusted depending on the distance between the image projection apparatus and the projection face. For example, the focus adjustment can be conducted automatically using a sensor, which is known as the auto focusing capability of the image projection apparatus. The auto focusing control operation can be performed by projecting a pattern image for the focus adjustment from the image projection apparatus, and capturing the projected pattern image by a camera of the image projection apparatus.
When the auto focusing control operation is performed based on a captured image of the projected pattern image, it is preferable to reduce or suppress fluctuation of the brightness of projection image. For example, as to conventional projectors, a pattern image projected on a screen is captured by a camera, and then the auto focusing control operation is performed based on an image captured by the camera, in which a driving waveform of a light source during the focus adjustment mode and a driving waveform of the light source during the normal operation mode are set differently to maintain brightness of image data of the projected pattern image used for the auto focusing control operation at a substantially constant level.
When the auto focusing control operation is performed by capturing the pattern image, the auto focusing adjustment is preferably performed during the warming-up mode of the image projection apparatus to reduce the time of completing the activation of the image projection apparatus. However, since the brightness of projection image fluctuates (i.e., brightness is not a substantially constant level.) during the warming-up mode, the pattern image cannot be captured correctly, and thereby the auto focusing adjustment cannot be performed effectively.